Electron-discharge apparatus



Dec. 20', 1927.

MILL! AMP.

W. K. KEARSLEY. JR

ELEGTRCN DISCHARGE APPARATUS Filed Sept. 2, 1924 Fig. 1.

2 Sheets-Sheet l Fig. 2.

so WITHOUT 67$45lL/ZER Inventor: William K. KearsIe Ar Hi6 Attorn e15.

Deaf-20, 1927. I '1;$53,102

Y W. K. KEAfRSLEYpJR- Y ELECTRON VQIIISGHARGE APPARKTUS Fig. 5.

Inventor 1 William K. KeorslegJr.

His Attorneg.

Patented Dec. 2a, 1927.

wires l star wrermm- K. KEARsLE i', 33,0? s'crrnri'noranif, l ili'iiii'"roiaaj ss eeea To ELECTRIC COMPANY, A conrojrterlloiv on NEW YORK.

ELECTRON-Disclaimer: Arman-Ares.

Application filed. September 2, 19242. Serial no'lt'saaee.

charge produced independently of gaseous.

ionization. It is the object of my invention lo to provide a method andmeans for automatically regulating the electron emission of the cathodeof a thermionic device to give a desired operatlng characterist c.

My invention is particularly applicable to the operation of an X raytube of the in cande'scent cathode type, and is embodied in an apparatuswhereby a constant" X-ray output may be secured even though the sourceof cathode heating current varies in voltage.

The novel features of my invention will be pointed out with greaterparticularity in the appended claims. For a better understanding of myinvention, reference may be had to the following description taken 1nconnection with the accompanying drawings in which Fig. 1 is a diagramof an X-ray system embodying my lnvention; Fig. 2 is a graph-ofelectrical characteristics of a? de-.

vice equipped with a stabilizer, as compared In) with the same devicenot so equipped 3 is adetail view of a vibrator 'used'm my tube 1 of thetype now known as the self rectifying Coolidge tube, is shown connectedto the high tension secondary winding of I 4o'tlie transformer 2, havingthe low tension primary circuit connected to a suitable source ofcurrent represented by mains 8, 4, carrying alternating current. TheX-ray tube 1 contains a cathode shown'in detailin Fig;

taining an inset 7 of refractory metal, pref erably tungsten. The anodeis preferably i i in good thermal relation to a radiator 8, butauxiliary devices such as this radiator, are

merely shown in thecdrawing as illustrating one complete embodiment ofmy invention. My invention is not confined inits function toan X-raytube,-but is applicable to other ustable;

. tacts 15,16 to'reducesparking.

r '4: consisting of a heated filament 5 surrounds ed by a focusingdevice 6 and an anode 7 consisting preferably of a. rodof coppcr.con-'forms of electron-discharge devices, diife'riiig in function andstructural details from an X ray tube. 7 I 1 I The cathode 5 of theX-ray tube is connectod by the conductors '9, 10 to the secondarywinding of a transformer 11, .the

primary of which is connected in series with a suitable adjustableresistance 12 to thesup ply ma ns 3, a. r-Xresis-tancelel' is included,111' the auxiliary heating circuit 9, .10 111 series with the secondarywinding of the transformer 11. In a shunt circuit to the re sistance 14are vibrating or make-and-break contacts 15, 16, one at .leastof whichis adlliese contacts 15, 16 are caused to open and close at a rapid rateduring the, operatioirof the tube, the relative durations of periods ofmake as compared withthe periods of break being determined by thestrength of the current flowing through an electromagne-t 17, thewinding of which is included in the circuit 18 carrying the cur rentflowing from cathode to anode through the. X-ray tube. One embodiment ofa vibrator magnet is shown in Fig; -Inv the apparatus illustrated inthis figure the vibrating armature- 19 of the magiietiopposes in itsdownward motion a springQO, the tensionof whichmay be adjusted by ascrew"21. Preferably the vibrator is adjustedtoi operatesubstantially insynchronism with the I alternating current supply. A condenser 22 may'beprovided connected across the con- Before.describing-the operation orfund tion of the apparatus illust-ratediby. Fig. 1, 1

attention is directed to the graph shownin' Fig; 2. In a system similarto tliefsystem shown in Fig". 1'. but in which the resistance 14c andthe shunt connected vibrating contacts 15, 16, are omitted, and in whichthe i i cathodezofgan electron dischargedevice is heated w thout: anyregulation .by current from a transformerv supplied from a sourcevarying'in potential, the load current flowing from cathode to anodethroughthe electron discharge device varies with the variations, I

of potential [of the cathode heating-current.

ata rate indicated by thecurve 28. The,

voltage across the terminals of the primary winding of the filamentheating transformer have been plotted in- Fig; 2' as abscissee through'arange of voltages :from 70 to 87.

ivolts, the corresponding current ,values be:

Lil

crease of about 5.1% the space current in creases from to milliamperes,an increase of about When a system such as above described having noregulator is connected to an ordi nary commercial transmission line,incidental voltage variations in these lines, espe' cially whencommercial devices such as elevator motors, are supplied by the samelines,

is suflicient to produce such wide variations in output of an electrondevice, such as an X-ray tube, as to make it difficult to deter mine aproper X-ray exposure.

When, in accordance with my invention, a device havinga cathode whichemits elec trons independently of ionization efiects and from whichhence a saturation current may be obtained, such for example as a hotcathode X-ray tube, is supplied with a stabilizer responsive in itsoperation to the load current passing through the device, thetransmitted current becomes substantially con stant with wide variationsof voltage. As shown, for example in the curve 24., an increase ofvoltage from 82 to 87 volts produces no, appreciable change of current,and

in fact, even an extreme increase of line voltage to 120 volts causes anincrease of current of only slightly more than one milliampere oranincrease of about 10% of current change with a voltage change of 46%.

- In commercial operation the filament heating transformer of an X-raytube probably.

would not be subjected in its primary voltage to :this wide variation.In practice,

therefore, over an operating range of say,;10

volts, the current through the tube is maintained substantiallyconstant. This action occurs by reason of the variations in magneticattraction of the core of the stabilizer magnet 17 upon the armature 19of the vibrator, as already indicated. The magnet 17 for any particularcurrent setting varies the effective length of the cyclic impulses ofvthe current fed to the cathode, the impulse of current depending induration on the conditions governing electron emission, thus heating thecathode to'the temperature required to maintain the desired currentvalue.

' By effective length of current impulses, I mean the length of thecurrent wave before it is reduced to a low value, as'when a resistanceis inserted in the circuit. For example, if the current has atendency toin-' crease the time required for the magnet 17 to build up to astrength required to open the contacts 15, 16' each wave of current isreduced. Hence, the contacts 15, 16 are open longer and the resistance14 is included in series with the circuit 9, 10 for relatively longerperiods, thereby weakening the cathode heating current sufficiently tooppose any further increase of thecathode temperature. Similarly, aslight decrease of current will result in weakening the magnet 17,thereby increasing the relative durations of the periods of closure of"the short-circuiting contacts and thereby strengthening the oathodeheating current. As the electron emissivity of the cathode varies at arapid rate directly with the temperature, this control of cathodeten'iperature by the vibrating stabilizer in the cathode heating circuitcontrols the electron'en'iission and hence the currentcarrying capacityof the X-ray tube. The stabilizer consequently maintains the currentreaching the anode at a predetermined value, I

as the described X-ray tube. isv operated at voltages at whichsubstantially all of the electrons emitted from the cathode'are utioccurin the electron emissivity of the cathode. 1 In some cases my inventionmay be "used advantageously in an 7 X-ray apparatus which has aresistance in series with the primary of the high voltage transformer inorder to limit the current which may be drawn from this transforn'ler. For example, in X- ray devices operating at exceedingly high voltages,say, for therapeutic purposes, such a resistance can be used to limitthe current to a value not fatal to life. My invention in such a systemcan be used to give a substantially constant current through the X-raytube instead of a. variable current as would otherwise be the case. p

In Fig. 5 l have illustrated an X-ray system suitable for operation witha regulable resistance 26 in series with the primary winding of. a highpotential transformer 27. The X-iay tube 28 in this case is con ected tothe secondary windings of the transformer 27in series with a mechanicalrectifier 29 driven by a synchronous electric motor 30.

Conveniently this motor is supplied with current by the conductors 31connected to the supply mains 32 in common with the X-ray transformer27. The cathode 5 of theX-iay tube is supplied with a heating current bya transformer 11 in the primary winding of which are vibrating contacts15, '16, con-. trolled by a magnet 17 connected by the con-- ductors 33,34, in series with the secondary coils 35, 36, of the X-ray transformer.A resistance 14 preferably is connected across the contacts 15, 16'.

The system shown in Fig. 5 is closely similar to'the system shown inFig. 1 except that the use of a resistance in the primary or" the maintransformer 27 renders the use of a special rectifier in series with theX ray tube desirable inorder to protect the tube from high potentialduring the periods of polarity reversal when a rectifying directconnected X-ray tube, as shown in Fig. l, is not taking current. V

In both the systems described, that is the systems shown in Fig. 1 andalso in Fig. 5,

the regulator maintains in response to space current flowing through theX-ray tube, an Xray output which s constant in quantity.

.In. these systems the energy input 'to the cathode is regulated tomaintain a constant em ssion of electrons regardless not only of voltagevarlations of the cathode heatlng source but also of variations ofconditions inthe X-ray tube-which affect the emissivity of the cathode,such for example, as the evointerior parts of the X-ray tube.

' 'stancy of electron emission at'the cathode and hence or quantityX-ray output, which of the Xray tube.

which the heating current is flowing.

is sutficient for some purposes, may be maintained "by keeping thetemperature of the cathode substantially constant, regardless of linevoltage changes. In that case the actuating coil of the regulator may beconnected directly tothe heating source for the cathode Such anarrangement is illustrated by Fig. 6, in which the actuating coil 17 isconnected by the conductors 38, 39 to the respective supply lines 3, 4E.The parts and electric connections otherwise correspond to the apparatusdescribed inconriection with Fig. 1. An X ray tube such as shown in Fig.5 may be used. Fluctuations oi supply voltage will advance or retard'theinstant the circuit is broken each half wave, thus increasing ordecreasing as required the. doles of current received by the cathode.For example, should the supply'voltage'rise, the 'coil 37 will cause thecontact 16 to open sooner, thus decreasing the periods. during. y reasonof the increased voltage the current rises at atast-e'r' rate and hence"energy delivered during these shorter periods remains unchanged. Byreason of the heat storage capacity oi the cathode, this internnttentheat input" will produce continuously a substantially constant cathodetemperature.

Conversely, a fall of voltage of the supply circuit will causethejperiods of cathode excitation to increase but without substantially"altering the:cathode 'temper'ature and hence. the electron emission. Asalready stated, constancy of vacuum and other tube condi tions areassumed to secure a constant quantity of X-ray output from the apparatusillustrated by Fig. 6. Y r

, It is obvious that various modifications, such for exalnpleas theabove described, may be made without departing from the spirit oi myinvention. a

hat I claim as new and'desire to secure by Letters Patent of the UnitedStates, is: 1. An Xray apparatus comprising the combination of an Xraytube having main" electrodes including a cathode which is heat-' ed; bypassage or current therethrough, .a main operating circuit connected tothe main electrodes of said tube, an independent heating circuitconnected to said cathode, a

source of alternating current subject to volt- I age variation forsupplying both circuits, and means responsive to load current in saidmain circuit'for reducing the current in said heating circuit :durln'geach half wave for periods of suchlength that the load. current ismaintained substantially constant.

.2. The combination of an electron discharge tube having a cathodeadapted to be heated by passage of current, an alternating currentsupply means for heatlng' sald cathode, and a. vibrating regulatorresponsive to load current in said tube and constructed to operate insynchronlsm with the current in said supply circuit for regulating V theheating'current to maintain the load current at a predetermined value. II

3. The combination ofan X-ray tube haw ing a cathode adaptedto beindependently. heated, a source of alternating currentsubject tovariations of voltage connected to operate said tube, means for derivingcurrent from said source toheat said cathode, and means responsive tocurrentthrough said tube for decreasing the heating current for saidcathode to a low vaiueduring each cyclic change of current i'or a periodor" suchlength that the current through said tube is maintainedsubstantially constant.

4. An X-ray apparatus comprising the combination ofan X-ray tube hav ngva cathode operable at incandescence, a main supply circuitftor saidtube,a heating circuit for Sfi-lClCEltllOdQ,-l resistance in saidheatingcircuit, a circuit containingmake and break contacts connected inshunt toisaid resistance,

and meansrespon'sive to an electrical condilac tion of the current insaid maincircuitfor varying the relative duration of the periods of makeand break of said contacts to control the heating current for saidcathode.

X-ray tube having a cathode adapted tobe independently heated and ananode, 1621118 for heating said cathode,- a main operating circuitconnected to the electrodes of said X-ray tube, and a vibratingregulator .arranged to maintain the electron emission 0]": said cathodeat a predetermined relation to an electrical characteristic of said maincircuit.

6. An X-ray apparatus comprising a source ct alternating currentsubjectto variations of voltage, an X-ray tube operatively connected thereto,said tube having a cathode i supplied 7 with heating current from saidsourceand means responsive to load current in said tube and operating insynchronism with said source for controlling the cathode heatingcurrent. I V ,7. An X-ray apparatus comprising an i tube having anincandescible cathoce and an anode, a main supply circuit connected tosaid electrodes, a circuit for supplyingheat ingf energy to saidcathode, vibrating contacts in said heating circuit, and electromagneticmeans responsive to current in said main circuit for regulating therelative duration of the periods of make and break off? said contactsthereby preventing departures oi current in said main circuit from apredeter mined value.

8; An X-ray apparatus adapted for opera tion ltrom a source ofalternating current of fluctuating voltage con'iprising the combinationof an X-ray tube of the Coolidge type operating substanti allyindependently of impactionization, a main stcp-up transformer having asecondary winding connected to the.

main. electrodes of said tube, an auxiliary transformer having awhirling connected to supply heating current to the cathode oi? sa dtube, a resistance in circuit with said winding, electric make and breakcontacts connected in shunt to said refstance, and electromagnetic meansin circuit *ith said X- ray tube tor operating said contacts in syntionfrom a source of variable voltage com- 7 prising an X-ray device havingan electrode capable ofeinitting electrons When heated, a main loadcircuit, a'heating circuit for said electrode, a resistance in saidheating circuit andelectromagnetic means responsive to the current insaid main circuit having contacts arranged to insert and Withdraw saidresistance intermittently, and means for controlling the relative duraton of the periods 0. An X-ray apparatus comprising an of insertion andwithdrawal to maintain the load current at a predetermined value.

10. An X-ray apparatus comprising an.

X-ray tube having a cathode adapted to be heated by passage ot currentand operating without substantial gas ionization, a source ofalternating current subject to variations variable voltage con'iprisingthe combination or" an X-ray tube'having a cathode adapted to emitelectrons when heatedby passage of current, means for deriving energyfrom the supply sourceto operate said tube, separate means for derivingenergy fromthe supply source toheat said cathode, and means oper- I atedby current from said source for intermittently reducing said cathodecurrent synchronously with the alternations of said source for periodsvarying in duration in such measure that the quantity of X-ray out putremains substantially constant When the voltage of said source varies.

12. The combination of an electron discharge device which" isconstructed and evacuated to be capable of operation substantiallyindependently of positive ionization, and having a cathode adapted togenerate electrons independently of a load current in said device, meansfor energizing said cathode with alternating current, and meansresponsive to a load currentin said device for varying the el'l'ectiveduration of the i cyclic impulses of said alternating circuit in suchmeasure that the load current is maintained substantially constant.

13. An Ix-ray apparatus adapted for operation from an alternatingcurrent supply source of variable voltage comprising the combination ofan X-ray tube provided with a cathode adapted to emit electrons Whenheated by passage of current, a main circuit coni cctedto the electrodesof said tube, a heating circuit for said cathode connected to derivecurrent from said source, and arranged for operation at voltages atwhich current in the main circuit is limited by electron emission of thecathode, and regulating means responsive to current in said load circuitfor decreasing the cathode heating current during each Wave of currentflowing therein for periods of such duration that the cathodetemperature and current in the main circuit will remain substantiallyconstant. 1

14. An X-ray apparatus adapted for operation from a source ofalternating current subject to variations of voltage comprising an X-raytube of the Coolidge type having a cathode operable at incandescence, ahigh potential transformer connected v.to said source for supplying saidtube with current,

circuit connected to said electrode,a-lternating current supply meanssubject to voltage variations for said heating circu t, and

electron'iagnetic means responsive to a load current in said tube andoperating in synchronismwith said heating current for varying theeffective resistance of said heating circuit during each wave of heatingcurrent for periods of such duration that the electron emission in saidX-ray tube and consequently the output of X-rays aremaintainedsubstantially constant.

16. The method of operating an electrical discharge device whichconsists in supplying energy to the cathode of said device at a ratewhich it continued would generate a greater supply of current carriersthan is required to maintain a desired current through said device at agiven voltage and intermittently reducing the supply of energy to saidcathode below the value required to maintain the desired current, saidreductions occurring during time intervals of the order of frequency persecond of commercial alternating current and varying the duration ofsaid intervals of energy reduction in such measure that a load currentof desired value can be maintained at a chosen impressed voltage.

17. The method of operating a thermionic discharge device which issubject to changes of operating conditions which consists in supplyingto the cathode of said device a heating current of materially highervalue than is required to give a desired electron emission,intermittently reducing said current at intervals recurring per secondwith a frequency of the order of cyclic changes of commercialalternating current and varying the relative duration of the intervalsof reduced current in such measure that-the load current in said deviceis maintained at a substantially predetermined value.

18. The method of operating a thermionic discharge device which issubject to changes electron emission of operating conditions whichconsist in supplying to the cathode of said device a cyclic current ofhigher value than requlred 'to heat said cathode'to a temperature givingdesired electron emission, materially reducing said current during eachcycle, and

varying the duration of the intervals of reduced current relative tointervals of-unreduced current in such measurethat the electron emissionof said cathode is maintained at a predetermined value.

19. The combination ofan electron discharge device having a cathodeadapted to be heated by passage of current, means for supplying aheating current to said cathode, means responsive to space current insaid tube for reducing the heating current to a low value at rapidlyrecurring intervals of such variable duration relative to the periods ofhigh current that a substantially uniform is obtained from said cathode.i

20. The combination of a thermionic X- ray device, a supply circuittherefor, means for supplying a heating current to said cathode, meansfor materially reducing said current at intervals recurring with afrequency of the order of commercial alternat ing current and meansresponsive to a space current in said device for varying the duration ofsaid intervals of reduced heating current relative to the unreduced'heating current to produce a desired electron emission by said cathode,whereby the X-ray output is maintained substantially constant.

21. An X-ray apparatus comprising the combination of an X-ray. tubewhich is operable independently of positive ionization and is providedwith a cathode rendered active by passage of current, means forsupplying a cyclic heating current to said cathode, and

means for regulating the effective value of said heating current in suchmeasure during the periods when said X-ray. apparatus is conductingcurrent that a constant current carrying capacity 1s maintained in theX- ray tube when changes occur in the electron emissivity of saidcathode or in the voltage of the cathode heating current.

22. In a system of theclass described, an

X-ray tube of the hot cathode type with a secondary of a step up'transfori'ner divided into two coils, a relay in'sai'd system with itsmagnet connected to said coils, a transformer for generating a hotcathode current and suitable connections including a resistance so thatwhen the system is in use the resistancewill be thrown in and out ofcircuit accordingtov the action of the relay -magnet..

In witness whereof, I have hereunto set my hand this 29th day of August,1924.

WILLIAM K. KEARsLErJR.

